1. Field of the Invention
The present invention relates generally to the field of submersible pumping systems of the type used in petroleum production and similar well applications. More particularly, the invention relates to a technique for protecting circuitry associated with such pumping systems, such as electronic circuitry for measuring or processing sensed or controlled parameters through the use of an inductor assembly.
2. Description of the Related Art
A variety of equipment is known and is presently in use for handling fluids in wells, such as petroleum or gas production wells. For example, a known class of such equipment includes submersible pumping systems, which typically comprise a submersible electric motor and at least one pump coupled to the electric motor. The pumping system may also include such equipment as motor protectors, fluid separators, and measuring or control equipment, such as digital or analog circuitry.
The equipment may be deployed in a wellbore in a variety of manners. For example, a submersible pumping system may be lowered into a desired position within a wellbore via a cable coupled to a wire line or similar deployment device at the earth's surface. Power and data transmission lines are typically bound to the suspension cable for conveying power to the submersed equipment, as well as for conveying control signals to controllable components, such as valving, instrumentation, and so forth, and for transmitting parameter signals from the equipment to the earth's surface. In an alternative technique, the equipment may be coupled to a length of conduit, such as coiled tubing, and similarly lowered into a desired position within the well. In coiled tubing-deployed systems, power and data transmission cables may be positioned outside the coiled tubing, or may be disposed within the elongated bore defined by the coiled tubing.
Once positioned in the well, circuits in the equipment are energized to perform desired functions. For example, in the case of submersible pumping systems, electrical power, typically in the form of three-phase alternating current power, is applied to the electric motor to drive the equipment in rotation. A pump thereby displaces wellbore fluids either through a stand of conduit to the earth's surface, or directly through a region of the well casing surrounding the cable or coiled tubing by which the equipment is deployed. Other well equipment may perform additional functions, such as reinjecting non-production fluids into subterranean discharge zones. In addition, powered well equipment may perform measurement functions, drilling functions, and so forth.
In an increasing number of applications, rather sensitive electronic equipment is deployed in wells along with powered equipment. Electronic circuitry associated with the equipment will typically perform measurement or controlling functions, or both. In such cases, it is often necessary to provide a desired level of electrical power to the electronic circuitry. This is advantageously done by means of a common cable assembly used to supply power to the driven equipment. In the case of submersible electric motors, one technique for supplying power to measuring and control circuitry includes superimposing a desired power signal on the alternating current power used to drive the electric motor. At a Y-point of the motor windings, the power can be tapped and fed to the electronic circuitry.
While it is advantageous to provide electrical power for monitoring and control circuitry by a power signal superimposed on drive power, this technique may call for protective circuitry in the event of certain failure modes. For example, where dc power is tapped from the Y-point of motor windings, a ground fault or loss of a phase in the motor drive circuitry can lead to referencing of the Y-point (i.e., a higher than desired power level at the Y-point). Such faults can cause damage to the downstream dc circuitry necessitating removal and servicing, and resulting in down time and maintenance costs. To protect the circuitry, inductors or chokes may be employed to prevent high voltage and current power from quickly entering the dc circuitry. However, existing choke structures do not typically provide sufficient protection for the circuitry. For example, in inverter motor drives, very high voltage spikes may occur at the Y-point of the motor windings, depending upon the failure mode. Such spikes can seriously damage conventional chokes. Larger or higher capacity choke structures may be provided, but these are typically limited by the dimensions of the wellbore, effectively limiting the options for increasing of the size or inductance of conventional choke structures.
There is a need, therefore, for an improved technique for protecting electronic circuitry supplied with power from powered equipment in well applications. In particular, there is a need for an improved structure which provides both dielectric strength as required by the anticipated level of voltage and current spikes, while providing sufficient inductance to dissipate power during such periods. There is also a need for a structure which can be manufactured and adapted to both new and existing applications, and which can be integrated into existing equipment envelopes, such as those dictated by the dimensions of conventional wells.